Movable barrier operators may be used to control access to areas by moving movable barriers between different positions. Movable barrier operators may estimate properties of the movable barrier such as position and speed by measuring, or deriving from a transmission of the movable barrier operator, the position and speed of an output of the movable barrier operator. However, the estimated properties of the movable barrier may diverge from the actual properties of the movable barrier due to changes in mechanical advantage throughout the path of the movable barrier.
For example, a jackshaft-style movable barrier operator may be installed in a warehouse or garage to control the position of a movable door. The jackshaft operator generally includes an output shaft connected to a counterweight shaft with a torsion spring that lifts most of the weight of the door. To control the position of the door, the jackshaft operator has a drum mounted on the shaft and a cable connected at one end to the drum and at an opposite end to the door. The jackshaft operator can rotate the drum to either wind up or pay out the cable from the drum and generate movement of the door.
The drum of a jackshaft operator may be conical so that a radial distance between the counterweight shaft and the drum surface portion where the cable is being wound up on or paid out from the drum changes as the cable is wound up or paid out. A conical drum may be advantageous in certain applications to provide a different moment arm for the jackshaft operator at different points in the door travel, e.g., the radial distance (and corresponding moment arm) is relatively small at the beginning of door travel when the door is at its heaviest and gradually becomes larger as the door gets lighter toward the end of the door travel. This constantly changing radius makes determining the position of the door based on the position of the output shaft difficult because the distance the door moves with a given amount of shaft rotation changes as the radial distance between the shaft and the drum surface portion (where the cable is being wound up or paid out) varies. Further, the constantly changing radius makes determining the speed of the door based on the speed of the jackshaft operator output shaft difficult because a given speed of rotation of the drum will produce a different speed of the door depending on the position of the door along its path.
Another problem with jackshaft operators is that drums come in a number of different shapes and profiles that allow an installer to select a drum best suited for the barrier and rail system of a particular application. However, from the perspective of a movable barrier operator manufacturer, the shape and profile of a drum that will ultimately be selected by an installer for a particular application is somewhat unknown. Thus, the ability of the movable barrier operator manufacturer to tailor the jackshaft operator to the drum is difficult and the jackshaft operator's understanding of the actual operation of the barrier is therefore less than optimal in some installations. Although the above discussion highlights jackshaft-style operators, the difficulty with estimating the position, speed, or other properties of a movable barrier is equally challenging for other types of movable barrier operators such as trolley style operators.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.